Search

In this study, the flow of Cu/oil nanofluids over an impermeable semi‐infinite plate was investigated. A complete single‐phase modeling of nanofluids flowing over a semi‐infinite plate was performed, bringing into account, real experimental data of oil‐based nanofluids. The empirical correlations revealed that the viscosity and thermal conductivity of the pure oil and oil‐based nanofluids strongly depend on temperature. The similarity transformation method was utilized to transform governing partial differential equations into coupled nonlinear ordinary differential equations solved by employing the standard Runge–Kutta. The results showed that even low volumetric fraction of copper/oil nanofluids noticeably enhanced the heat transfer; however, such behavior was not predicted accounting the classic modeling of nanofluids. Furthermore, both hydrodynamics and thermal characteristics were reliant on the thermal boundary conditions, which this seems to have received a marginal focus in the existing literature. [ABSTRACT FROM AUTHOR]

The present work provides an empirical investigation on the thermal characteristics of Ag/oil nanofluids flow inside a sinusoidal tube under a constant heat flux boundary condition. Ag/oil nanofluids have been prepared in low-volume concentrations of 0.011%, 0.044%, and 0.171%. The average size of the nanoparticles was 20 nm. A heated coil was attached to the upper and lower surface of the tube that satisfied the constant thermal boundary condition of 204 W. The experiment has been pursued at low Reynolds numbers less than 160. A loop was designed to keep the flow hydrodynamically fully developed during the experiment. The test case was a sinusoidal tube. Upper and lower surfaces of the tube have been designed sinusoidally. Moreover, the width of the plates was long enough, so the problem was not considerably affected by the three-dimensional releasing effect. Convective heat transfer coefficient and Nusselt number were calculated. It has been observed that based on the acquired data of the present work, convective heat transfer coefficient increased up to 23% for the best case (nanofluid with a volume concentration of 0.171%) compared to the base fluid. This happened while the rise of the friction factor was very low. In addition, a comparison between the new results and the previous work by authors showed the positive performance of sinusoidal tubes in increasing the convective heat transfer coefficient (the average increase was calculated to be about 82%) compared to the annular tube. [ABSTRACT FROM AUTHOR]

The present study indicates the impact of different arrangements of dielectric barrier discharge (DBD) plasma actuators on temperature field in a channel flow. The modified lumped circuit element electro-static model was used to calculate induced Lorentz body force and plasma dissipation of the actuators. Different distributions of temperature in the modeled channel flow for each arrangement of actuators (one, two, and three attached actuators) are discussed. According to the numerical simulation, DBD plasma actuators are beneficial devices for increasing temperature in the channel flow, especially near the location of the actuators that can be considered for related applications. The actuators are modeled under an incompressible flow regime with low Reynolds number of 335, and the configurations of the actuators are set to be 3 KV for the peak voltage amplitude, 10,000 Hz for the voltage frequency, and Kapton as the dielectric. [ABSTRACT FROM AUTHOR]

This study deals with an empirical investigation on the convective heat transfer of Cu/oil nanofluid flow inside a concentric annular tube with constant heat flux boundary condition and suggests a correlation to predict the Nusselt number. The average size of particles was 20 nm and the applied nanofluid was prepared by Electrical Explosion of Wire technique with no nanoparticle agglomeration during nanofluid preparation process and experiments. The nanofluid flowing between the tubes is heated by an electrical heating coil wrapped around it. The effects of different parameters such as the flow Reynolds number, tube diameter ratio, and nanofluid particle concentration on heat transfer coefficient are studied. Using the acquired experimental data, a correlation is developed for the estimation of the Nusselt number of nanofluid flow inside the annular tube. This correlation has been presented by using the exponential regression analysis and least-squares method. The correlation is valid for Cu/base oil nanofluid flow with weight concentrations of 0.12, 0.36, and 0.72 in the hydrodynamically full-developed laminar flow regime with Re <140, which is applicable in mini- and microchannel heat exchangers, and it is in good agreement with the experimental data. [ABSTRACT FROM AUTHOR]

In this study, thermo-physical properties including thermal conductivity, viscosity, density and specific heat capacity of an oil based nanofluid including silver as to be nanoparticles have been experimentally studied. The results indicate an enhancement in thermal conductivity which was depended on bulk temperature and volume fraction of utilized nanofluids. Viscosity data show a significant increment through volume fraction increasing. In addition, the specific heat capacity and density of nanofluids were studied experimentally and it was found that, all measured rheological properties of these nanofluids, were not in agreement to published correlations. [ABSTRACT FROM AUTHOR]

An oil based nanofluid including silver as to be nanoparticles was created by EEW method as a one-step method in three different volume fractions have been experimentally studied. Assessing the stability and viscosity of the nanofluids was involved in this work. The results show that the nanofluids behave in both of Newtonian and non-Newtonian in different volume concentrations. Also, an enhancement in viscosity of nanofluids has been recognized. In addition, based on the experimental results of this study and the other previous published studies on the oil based nanofluids, a correlation for predicting viscosity of oil based nanofluids has been developed and a good agreement between the experimental viscosity of applied nanofluids in this study and the predicted one has been achieved. [ABSTRACT FROM AUTHOR]